I was flying SJU-MIA-LAX on Saturday (AA1091, AA275), both were purchased in I (Business). Because of the MX delay on the inbound flight for AA1091, I was going to miss my connection in MIA. At the check-in counter, the agent noticed that I was put on AA1147, but in B class, and without a seat assignment. Fortunately, the SJU station manager was at the counter (dealing with the delayed 1091 as well as the SJU-JFK that was dinged with a 3 hour delay), so he was able to override the re-ticketing and eventually re-issued the ticket into I class.